/**
 *    Copyright (C) 2019-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include <type_traits>
#include <typeinfo>

namespace mongo {

/**
 * Will cast pointer 'a' of type A* to type B* if 'a' points to something that is _exactly_ a 'B'
 * (not a sub-class of B).
 */
template <class DerivedPtr, class Base>
auto exact_pointer_cast(Base* b) -> DerivedPtr {
    static_assert(std::is_pointer<DerivedPtr>::value);
    using Derived = typename std::remove_cv<typename std::remove_pointer<DerivedPtr>::type>::type;
    static_assert(std::is_final<Derived>::value);

    if (b == nullptr) {
        return nullptr;
    }

    if (typeid(*b) == typeid(Derived)) {
        return static_cast<DerivedPtr>(b);
    }

    return nullptr;
}
}  // namespace mongo
